ASTR 380 Terraforming Other Planets

ASTR 380
Terraforming Other Planets
http://mensa-barbie.com/bloggerimages/468-Solarsyst_new_world_gliesesyst
Outline
Definitions and context
Terraforming Mars
The far future
Habitable Planet
“Class M” planets of
Star Trek
Basically, step on,
take a satisfying
breath, and start
colonizing!
Don’t know how
common these are
Biocompatible Planet
Planet with physical parameters to be habitable
Doesn’t have to be life on it now
Classic example: Mars, which we will now
consider in detail
Terraforming
Mars
Shaun Moss
Mars Society Australia
[email protected]
June 2006
Goals of Terraforming
A planet that supports life from Earth:
Temperatures approx. 0±40°C
Abundant liquid water
Breathable air
Fertile soil that supports plant growth
Sunlight
Walk on the surface without a spacesuit.
Why Mars?
Not too far from the Sun
Approx. 24 hour diurnal cycle
Not excessively cold (-140°C .. 20°C, avg -63°C)
Has water, CHNOPS, metals
Has seasons like Earth
Can hold an atmosphere
Because we think we can
Usual Approach
Warm Mars by several degrees.
CO2 and water vapour sublime from polar caps and regolith.
Greenhouse effect warms planet further, releasing more CO2 and
water vapour, generating more heat and so on: “runaway
greenhouse”.
Liquid water becomes more prevalent on the surface.
Introduce life. Photosynthetic organisms convert CO2 into O2.
Eventually atmosphere and temperature suitable for animals, including
humans.
Flowchart
Goal is a self-regulating equilibrium, probably best
achieved by a well-designed, stable, global biosphere.
Note addition of N2 importation – to be discussed.
3 primary planetary engineering tasks:
1
3
2
Task 1:
Increasing Temperature
Bulk of T increase comes from
greenhouse effect.
Some initial warming required to kick-start.
Popular ideas:
Space-based mirrors
Greenhouse gases
Albedo reduction
The New Phobos:
Mars’s 2nd Sun
Phobos’s orbit in decay.
Move Phobos into a higher, stable orbit. Repositioning minor
planets already examined in context of NEOs.
Better yet, move Phobos into a stable polar orbit, and cover its near
side with array of mirrors.
Sunlight reflected down onto both poles ~3 times per day, all year
round. Triggers sublimation of CO2 and water vapour.
Each mirror on a 2-axis mount, computer-controlled to track the
Sun. Solar-powered system.
Phobos only 22km diameter, but could extend mirror array wider by
building a framework into space.
Primary advantage: Phobos provides a source of material for
mirror fabrication, e.g. Fe, Al
Phobos appears like a second sun with half diameter of Sol,
travelling from N to S.
Phobos Mirror
Greenhouse Gases
CFCs excellent GHG, but short-lived in high-UV, also
ozone-depleting.
PFCs much longer-lived, 6500-9200 times more
effective than CO2 and non O3-depleting. Could build
PFC factories.
O3 good greenhouse gas which increases with O2
levels, and also needed to provide radiation protection.
NH3 obtainable from asteroids.
Methane: CH4 is 23 times more effective GHG than CO2
Cheap: can be produced industrially from H2 and CO2 (ISPP).
Can also be manufactured biologically.
Non-toxic and increases ozone production.
Introduce Methanogens
Extremophilic methanogens could be engineered to live
on Mars and produce methane. Stage 1 of biosphere.
Subsurface first (chemotrophic), surface later
(phototrophic).
Might already be there. CH4 in Martian atmosphere is a
clue.
If so, extant organisms could be made more prolific
and/or, might spread as planet warms and more H2O.
Methanogens are anaerobic and will die out as O2 levels
rise, unless new strains are engineered.
Albedo Reduction
Prev suggestions:
Dark-coloured algae/lichen.
Spreading black dust on poles – unfeasible in
Martian winds.
Longer-term solution:
Engineer plants with dark-green leaves.
Can offset T drop as CO2 levels decrease.
Summary: Warming
1. Phobos mirrors. Triggers global
warming.
2. Early biosphere: methanogens.
3. Long-term warmth: plants with darkgreen leaves; also aerobic methanogens.
Task 2:
Atmosphere Engineering
Mars’s atmosphere almost wholly CO2, small amounts
of N2 and Ar, trace elements of other gases.
However, very thin: only ~0.8kPa.
Ideally, terraformed atmo will be like Earth’s: 79kPa N2,
21kPa O2. What’s the minimum?
Require at least 16kPa O2 = minimum safe breathable
partial pressure of oxygen.
Equivalent to altitude of about 3km on Earth. (About
20% of newcomers would experience altitude sickness.)
O2 manufactured from CO2 by photosynthetic organisms.
Nitrogen
Mars has only 2.7% atmospheric N2 and unknown
quantities of other N compounds.
Importance of N2 frequently overlooked by terraformers.
Nitrogen fundamental to all DNA-based life, component
of amino acids & nucleic acid bases. Probably
insufficient nitrogen for planet-wide biosphere.
On Earth, N2 also serves as a buffer gas, reducing
oxygen toxicity, fires and corrosion. O2 levels higher
than 35% cause spontaneous combustion of biosphere.
We need more N2 .
How Much Nitrogen?
Need approx. at least twice as much buffer gas
as O2 to prevent fires, i.e. 32kPa.
Noble gas (e.g. He, Ne, Ar)? N2 is much easier
to source, plus required by biosphere.
Total minimum surface pressure for 2:1 N2/O2
atmo is ~48kPa (less than half Earth’s). A 3:1
mix (64kPa) would be better, 4:1 best.
(For H&S, keep thickening atmosphere beyond
terraforming goals until same as Earth.)
Bare minimum atmosphere:
O2: 6.85x1017 kg
N2: 1.2x1018 kg
Where to get all this N2?
3 options:
Earth
Venus
Titan
Earth – unlikely, probably cause global climate change.
Venus – close, but requires separation of 3.5% N2 from
96.5% CO2. (This option better if simultaneously
terraforming Venus.)
Titan – atmo 98.4% N2, remainder CH4 (which we like).
Far away, but robotic atmosphere-mining tankers would
have simple design. Just fly through atmo and fill the
tanks.
Mining Titan’s Atmosphere
Titan’s atmo contains approx. 9x1018 kg N2 and we want
1.2x1018 kg N2, so we are talking about transporting about
~13% of it to Mars.
How long will it take?
Let’s say, 1st year we build 5 spherical tankers with
r=100m. Est. round-trip to Titan = 10y.
Tech improves yearly. On average, every
year we build 10% more ships than the
previous year, with 10% larger radius, &
decrease round-trip time by 10%....
Have obtained required N2 in just 4 decades.
Even if it takes 2-3 times this long, this is not
excessive compared to other tasks.
Managing CO2 & O2 Levels
Will we have enough CO2?
CO2 may not come out of regolith easily.
CO2 dissolves in water, the colder the better. As hydrosphere expands,
CO2 levels will drop & not replaced by O2.
In water, CO2 can react with minerals to form carbonates – hard to
return these to atmosphere. (High acidity may inhibit carbonate
formation)
Will we have too much CO2?
Estimated 40kPa CO2 can be sublimated if loosely bound in regolith.
But we only need 16 - 21kPa O2.
Maximizing phytoplankton mass can offset carbonate production by
converting dissolved CO2 to O2.
Some bacteria can liberate CO2 from carbonate rock.
O2 can be produced by electrolysis or metal refining.
Can always get more CO2 from Venus.
Get the N2 first
Maximum safety:
Biological O2 pump hard to stop/control. If O2
levels exceed ~35%, risk of fires & damage
to biosphere, machinery, bases. Many
colonists by this stage.
Must ensure sufficient quantities of buffer gas
during warming and biosphere construction.
Also: the sooner we can start getting, N
compounds into the soil the better.
Plan 1: Warming First
Pros: Warm & wet early.
Cons: High risk of fires leading up to and
during Phase 3.
Plan 2: Get N2 First
Pros:
Atmosphere thick early (aids construction, improves safety).
Buffer gas in place.
Can start getting nitrates into soil sooner.
Allows for a long period of Mars research before more
serious climate change.
Cons: Cold and dry for a bit longer.
Plan 3: Concurrent Phases
Pros:
Faster.
Warm & wet early.
Atmosphere thick early.
Nitrate production.
Buffer gas in place; O2
always <35%
Cons:
Fire risk if N2
importation system
breaks.
Task 3:
Biosphere Construction
Start at the bottom of the food chain and
work up:
Basic chemical nutrients.
Microbes  Plants  Animals
Each generation improves environment for
next.
Aquatic vs. Terrestrial
Ecosystems
Aquatic ecosystems will develop before terrestrial (land-based).
Just like Earth:
1.
2.
3.
4.
Life began in oceans: protection from UV, availability of nutrients.
Aquatic plants converted CO2 atmo to O2.
O3 layer formed, providing UV protection.
Life moved onto land.
Mars cold & dry: aquatic bio-density will be greater than terrestrial.
C.f. Earth:
Much more aquatic life at poles than at equator.
Why? CO2 dissolves better in cold water, improves conditions for
phytoplankton, and hence higher organisms.
Much less terrestrial life at poles than at equators.
Why? Too cold and dry.
Martian Microbes
Primary engineers of planet.
Role is to prepare environment for plants.
Require ecosystem that performs a variety of roles:
Nitrogen-fixing
Nitrification
Methanogenesis
Alkalisation
Genetic Engineering – combine DNA from:
Functional organisms
Extremophiles
Extant Martian life
Functional Microbes
Nitrogen-fixing & nitrification: Azotobacter,
Rhizobium, Nitrosomonas, Nitrobacter, etc.
Chemoautotrophs/lithotrophs:
obtain E from inorganic molecules
synthesise organic molecules from CO2.
Methanogens – anaerobic, suited to low O2,
produce CH4.
Extremophiles: Categories
halophiles (salt)
acidophiles (acid)
cryophiles (cold)
xerophiles (dryness)
oligotrophs (lack of nutrients)
radioresistant (radiation)
Extant Martian Life
Will have useful genetic material, adapted for Mars.
Probably lives below surface, and therefore
chemotrophic.
Cryophilic.
Could be endolithic (living in rocks) or aquatic (subsurface pools).
Possibly methanogenic (low O2 levels, plus would
account for CH4 in atmosphere).
Combining Martian DNA with Terran species to create
new organisms preserves genetic heritage – “managed
evolution” may address moral question.
Martian Plants
Aquatic species
Most important – these convert atmo. Hence the need to
maximize wet areas by warming.
Phytoplankton (diatoms, dinoflagellates, cyanobacteria).
Macroscopic algae: kelp.
Tundral species (cryophilic)
Arctic, Antarctic & Alpine ecosystems.
Mainly lichen, mosses, grasses, some flowers and woody
plants, close to ground.
Lack of pollenating insects has caused evolution of vegetative
methods of propagation, e.g. underground runners, bulbils,
viviparous flowers.
Desert species (xerophilic)
Cactii.
Fast Biosphere Propagation:
Robotic Gardeners
Robots very advanced at time of
terraforming, esp. on Mars.
Can greatly increase biosphere
expansion rate.
Colonies maintain farms of algae and
other Mars-successful species.
Satellites in Mars’s orbit detect water,
measure heat/O2 output, growth rates.
Data used to direct highly mobile
robots (e.g. helicopters/balloons) to
carry seeds/spores to best areas.
Humans do research, but global
gardening system can be fully
automated.
Martian Animals
Special purpose:
Stingless bees – pollenation
Earthworms – soil manufacture
Granivorous birds – seed propagation
Aquatic:
Zooplankton, krill, squid, cold-water fish.
Terrestrial:
Fish-eating birds, land mammals, etc. from polar
environments.
First mammals: cats and dogs descended from
colonists’ pets.
Radiation Protection
Increasing O2 levels build ozone layer.
A magnetic field can be created by
building a planet-circling conductor.
Doubles as backbone for Martian power
grid.
Mars Prospects
Terraforming Mars requires a range of solutions.
Three basic planetary engineering tasks.
Phobos a useful platform for space mirrors.
Need to ensure nitrogen levels high enough to
dilute O2, reduce fire risk.
Use Solar System resources, not just Mars.
Robotics and genetic engineering key
technologies for biosphere construction.
Every task affects the whole planet – all parts of
process need to be managed concurrently.
Colonies on Venus?
Terraforming Venus
is much tougher!
But at 50 km, temp,
pressure is like Earth
Normal O2:N2 mixture
floats
Could have giant
floating cities in
atmosphere!
Methane_Harvester_final_by_gusti_boucher.jpg
Future Nanorobots?
Far future!
Might we make
nanorobots that copy
themselves and
terraform planet?
Exponential increase,
so this could be fast
Send out ahead of
colony ships!
http://www.acceleratingfuture.c om/michael/blog/images/bionanotechnology.jpg
Summary
Terraforming Mars, though extended and
hugely expensive, is within reach
What are benefits and costs?
Ethical questions: do we have right to
modify planets like this?